Tip clearance is the distance required between the blade tip and the pump body wall of an impeller in a helicon-axial multiphase pump, which tends to induce tip leakage flow. The tip leakage vortex formed by the interaction of tip leakage flow with the mainstream can seriously affect the performance of the multiphase pump. To minimize the adverse effects of tip leakage flow in the multiphase pump, a method to design a squealer tip on the impeller blade is proposed in this paper. The effect of the squealer tip on external characteristics, tip clearance flow characteristics, and energy dissipation of the multiphase pump is analyzed. Research results indicate that the blade squealer tip can effectively improve hydraulic efficiency of the multiphase pump. At the optimal efficiency point, the head and hydraulic efficiency of the multiphase pump with a squealer tip increased by 3.62% and 4.15%, respectively, compared with the original model. The influence of tip leakage flow in the axial rear half passage of the multiphase pump impeller is far greater than that in the axial forward half passage, especially on the back position in the middle of the impeller passage. The squealer tip can restrain the reverse of leakage flow from the pressure side to the suction side of the impeller blade, and the clearance leakage flow of the model with a squealer tip is smaller than that of the original model. The squealer tip on blade will reduce the energy dissipation caused by unsteady flow in the mainstream. The research results in this paper can provide theoretical support for effectively restraining the influence of the tip leakage vortex on the mainstream of the helicon-axial multiphase pump and contribute to engineering practice value of improving the performance of the multiphase pump.

To clarify the mechanism of gas plugging caused by gas–liquid separation in a helical axial multiphase flow pump under two-phase conditions, the flow pattern, bubble distribution, and evolution in the pump were studied by high-speed camera technology. It is found that the gas phase presents four different forms with different inlet gas volume fractions: isolated bubble flow, linear bubble flow, airbag flow, and emulsion flow. The increase in inlet gas volume fraction promotes the aggregation of bubbles and changes the flow pattern inside the impeller. This change can be alleviated by increasing the rotational speed to promote bubble breakup. In addition, the probability density function of the equivalent diameter of the bubble in the impeller obeys the lognormal distribution, and the equivalent diameter ranges from 0 to 4 mm. The equivalent diameter of the bubble is proportional to the inlet gas volume fraction and inversely proportional to the rotational speed. The bubble behavior is unstable, and it is easy to agglomerate at the inlet and outlet of the impeller to form large bubbles, which leads to a decrease in pump performance. This study provides a scientific basis for the optimal pump design and is of great significance for preventing gas plugging.

To investigate the effect of tip clearance on the velocity distribution in a multiphase pump, the internal flow and velocity distribution characteristics in pump under different tip clearances are studied using experimental and numerical methods. Simulations based on the Reynolds-Averaged Navier-Stokes equations (RANS) and the standard k-ε turbulence model are carried out using ANSYS CFX. Under conditions of inlet gas void fraction (IGVF) is 5% at the flow rate of 0.6Q, 0.7Q and 0.8Q (Q is the design flow rate), the accuracy of the numerical method is verified by comparing with the experimental data using high-speed photography. Results show that the leakage flow interacts with the main flow and evolves into the tip leakage vortex (TLV). Due to the TLV, the pressure, velocity, turbulent kinetic energy (TKE), vorticity and streamlines on the S2 stream surface in the impeller and diffuser are changed greatly under different tip clearances. The velocities at the impeller outlet and diffuser inlet along the radial direction are also changed. The axial velocity distribution is similar to the meridional velocity distribution at the impeller blade outlet. While the relative velocity and absolute velocity distribution show the opposite trends. In addition, the vorticity is larger near the tip separated vortex and the hydraulic loss in pump is also increased due to the TLV.

In a multiphase pump, tip clearance is the required distance between the blade tip and the pump body wall of the impeller, forming tip leakage vortex (TLV), causing unstable flow and energy dissipation. In the present work, the enstrophy dissipation theory is innovatively applied to quantitatively study the energy dissipation of the TLV. The flow rate, tip clearance, and inlet gas void fraction (IGVF) play a crucial role in affecting the enstrophy dissipation of the TLV. The results show that increasing flow rate, tip clearance, and IGVF significantly exacerbate the TLV pattern and raise the TLV scale, which gradually raises volume enstrophy dissipation and decreases wall enstrophy dissipation. As the flow rate increases, the separation angle between the primary TLV trajectory and the blade gradually decreases, and widely dispersing the enstrophy dissipation near the shroud. However, as the tip clearance increases, the tip separated vortex scale increases and extends to the suction surface, raising the velocity gradient. Besides, as the IGVF increases, the secondary TLV develops from a continuous sheet vortex to a scattered strip vortex, increasing the significantly increasing the enstrophy dissipation. Considering the flow rate, tip clearance, and IGVF as independent variables, simple and multiple nonlinear regression models have the ability to predict the enstrophy dissipation of the TLV accurately.